Self Selection Trial of Naproxen Sodium: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Self Selection Trial of Naproxen Sodium (NCT01383486), a non-randomized phase 3 study. The primary outcome is The Percentage of Participants Who Selected Naproxen Sodium ER and Expected Their Pain to Last More Than 12 Hours.

2. Clinical Question

The trial addressed a self-selection question rather than a conventional comparison of treatment outcomes. Its stated purpose was to assess whether consumers could appropriately select Aleve 24 Hour for their own use based on expecting pain to last more than 12 hours. Participants reviewed the product packages and chose one product upon a pain episode. The primary endpoint therefore describes the expectation associated with participants’ selection of naproxen sodium extended release.

This framing matters when interpreting the endpoint. It does not ask whether naproxen reduced pain, whether it was more effective than Advil, or whether expected pain duration matched a later clinical outcome. The endpoint is a percentage within the subgroup who selected naproxen sodium; it does not describe all enrolled participants. The registry record does not report the primary endpoint’s observed percentage, so the extent to which participants selected the product while expecting pain to last more than 12 hours cannot be assessed from the reported information.

3. Trial Design

This was a phase 3 pilot trial with non-randomized allocation, no masking, and a parallel model. The registry lists enrollment of 253 and a completed status. The recorded start was 2011-07, and primary completion was 2011-08. The sponsor was Bayer, and the listed condition was pain.

Eligible subjects were provided with 24 Advil immediate-release caplets containing 200 mg ibuprofen and naproxen sodium extended-release tablets containing 660 mg naproxen sodium. Upon a single incidence of pain, subjects were instructed to review both packages and choose one product to use. The recorded description ends before completing its final phrase, so further details of the instructions are not reported in the registry record.

The primary endpoint was collected through a toll-free interview. Participants were instructed to call within 30 minutes of their selection decision. Participants who did not call were interviewed after 14 days for data collection. The endpoint description specifies that the analysis included only subjects who chose naproxen sodium.

Because allocation was not randomized, selection of a product was a participant decision rather than an assigned treatment. The trial therefore does not support a randomized comparison between naproxen sodium and Advil. Preferences, expectations, or other factors could distinguish people choosing one product from those choosing the other, and the registry record does not report a design intended to balance such differences. Masking was none, which is consistent with participants reviewing packages and choosing a product, but details beyond the registry description are not reported.

The registry lists three outcome measures, including the primary endpoint and two secondary outcomes concerning selection of naproxen sodium among participants expecting pain to last more than 12 hours, with one secondary outcome referring to low-literacy participants. It lists zero analyses. Numerical results for the primary and secondary outcomes are not reported in the registry record.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: 435 subjects were screened, 384 were qualified for participation, 259 subjects presented at pharmacy to begin enrollment procedures, 254 gave inform consent, 1 subject refused to give pregnancy test, so 253 subject received the investigational products.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Only subjects who chose naproxen sodium were included in the analysis.

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as The Percentage of Participants Who Selected Naproxen Sodium ER and Expected Their Pain to Last More Than 12 Hours, measured over up to 14 days.

The primary endpoint is the percentage of participants who selected naproxen sodium extended release and expected their pain to last more than 12 hours. Its stated timeframe was up to 14 days. Participants were asked to select a product for use upon a pain episode and report their decision in an interview. The endpoint description says that those who did not call within 30 minutes were interviewed after 14 days for data collection.

The calculation is restricted to participants who chose naproxen sodium. Within that selected group, the numerator is the number who reported expecting pain to last more than 12 hours. The denominator includes those who chose naproxen sodium and reported an expected duration either greater than 12 hours or less than or equal to 12 hours. The endpoint is thus a conditional percentage: it describes expectations among naproxen selectors, not the percentage of all enrolled participants who made that selection.

This measure was used to address the trial’s self-selection aim: whether consumers chose the extended-release product when they expected a longer duration of pain. It captures a reported expectation linked to a product choice. It does not measure pain relief, duration of pain actually experienced, adherence, or comparative treatment effect. The observed percentage and its precision are not reported in the registry record, so the result cannot be quantified from the record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The statistical interpretation begins with the type of question the trial asked. This was a self-selection study: participants reviewed packages and chose a product when they experienced pain. The primary endpoint then focused on participants who chose naproxen sodium extended release and described their expected pain duration. It is a percentage endpoint, meaning that the quantity of interest is the share of a defined group meeting a specified condition.

What does a conditional percentage mean?

A conditional percentage describes a subgroup, not necessarily the full enrolled population. Here, the analysis population for the primary endpoint was restricted to subjects who chose naproxen sodium. Within that group, the endpoint counts those expecting pain to last more than 12 hours relative to those reporting an expectation either greater than 12 hours or less than or equal to 12 hours. People who selected Advil are outside that stated primary analysis population. The result, if reported, would therefore not answer what percentage of all participants selected naproxen sodium.

This restriction is central to interpretation. Product selection is part of the process under study, and it also determines who enters the primary endpoint calculation. A conditional percentage can be informative for the question it was designed to answer, while remaining distinct from a general rate across everyone enrolled. The registry record does not report the number of naproxen selectors or the endpoint percentage, so neither the subgroup size nor the observed proportion can be assessed from the record.

What does non-randomized allocation imply?

In a randomized comparison, allocation is assigned by a random process, which can help make treatment groups comparable on average. This trial instead allowed subjects to choose between naproxen sodium extended release and Advil immediate release. The choice could be related to participants’ expectations or other factors. Thus, a comparison between people choosing the different products would not have the protections of randomized allocation.

General statistical principle: an observed difference between self-selected groups can reflect both the product received and characteristics associated with choosing it. Statistical adjustment may sometimes address measured differences, but it cannot automatically remove unmeasured differences. The registry record lists zero analyses and does not report adjusted comparisons or a plan for such analyses. In any case, the stated primary endpoint is not a product-to-product comparison.

How should precision be understood?

General statistical principle: a confidence interval describes a range of values compatible with the data under the assumptions of the analysis. A narrower interval indicates greater precision; a wider interval indicates less precision. A point estimate alone would not convey how uncertain a percentage is. No primary endpoint estimate or confidence interval is reported in the registry record, so the precision of the self-selection result cannot be evaluated.

A percentage based on a subgroup depends on the information available within that subgroup. When the subgroup is small, estimates may be less precise; when it is larger, estimates may be more precise, all else being equal. This is a general explanation, not a claim about the size or precision of this trial’s naproxen-selected subgroup, which is not reported in the registry record.

What do planning calculations represent?

The stated sample-size assumptions describe a planning illustration based on the observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is described as a stated fraction of the observed effect. These assumptions are not reported as the trial’s own design justification. The registry record does not report a sample-size justification, and the actual planning values are not present in the registry information.

General statistical principle: a planning calculation estimates the sample size that would be needed under specified assumptions. It is not a count of participants who experienced an outcome, nor is it a measure of the probability that a completed study has established a result. If based on an observed effect, such calculations are illustrative and depend on that effect estimate and the chosen assumptions. They should not be called observed power. The record does not report the trial’s own sample-size rationale or a prospective target tied to a stated effect.

The planning assumptions refer to equal allocation between two arms, but the trial itself is recorded as non-randomized and involved product selection. A planning scenario should not be mistaken for a description of the actual allocation process. It also cannot transform the self-selected groups into randomized comparison groups.

What can be inferred from the registry’s analysis listing?

The record lists three outcome measures and zero analyses. This means the registry information includes endpoint descriptions but does not provide a listed analysis result. It does not establish whether analyses were performed outside the registry, and the record does not report why results are absent. The primary result, uncertainty estimates, and statistical tests are not reported in the registry record.

For the safety counts, simple event totals are available, but the record does not provide a comparative model or product-specific allocation. General statistical principle: event counts and risk comparisons are different kinds of evidence. A count can describe what was recorded in a group, while a comparison requires suitable groups and an analysis that accounts for the design. The safety figures should therefore be read descriptively and within the limits of the listed group.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Naproxen Sodium ER (BAY H6689) or Advil IR")
n      <- c(182)
events <- c(131)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Naproxen Sodium ER (BAY H6689) or Advil IR  182  131  72.0  64.9  78.4  65.1  78.0  65.0  78.0

11. Multiplicity, Missing Data and Analysis Populations

The registry lists three outcome measures: the primary self-selection percentage and two secondary outcomes. The secondary measures concern participants who selected naproxen sodium and expected pain to last more than 12 hours, including a measure for low-literacy participants and a measure that also specifies reporting the decision within the first 24 hours. The registry record does not report numerical results for these outcomes.

When a study evaluates multiple outcomes or conducts multiple statistical tests, the chance of at least one apparently notable result can increase. General statistical principle: multiplicity procedures can be used to control the interpretation of repeated testing, but the appropriate approach depends on the prespecified analysis plan and study objectives. The registry record does not report a multiplicity strategy, a hierarchy for testing outcomes, or an analysis plan. It is not possible to determine from the record how multiple outcomes were handled in any analysis.

The record lists zero analyses. It does not report the primary outcome estimate, confidence interval, test result, or missing-data method. The endpoint description says participants who did not call within 30 minutes were interviewed after 14 days for data collection, but it does not explain how unavailable interviews or incomplete responses were handled. The record does not report the number of missing endpoint observations or whether any imputation or sensitivity analyses were used.

The primary analysis population is defined as subjects who chose naproxen sodium. The record does not report the size of that population or a separate intention-to-treat analysis population. Because selection determines inclusion in the primary endpoint, the result would apply to the specified naproxen-selected subgroup rather than automatically to all enrolled subjects. The registry record also does not report whether any participants were excluded for reasons other than product choice.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry records zero serious adverse events among 237 participants at risk in the listed group. It records 14 other adverse events among 237 participants at risk in that same group. The group is titled Naproxen Sodium ER (BAY H6689) or Advil IR, so these figures are presented for the combined listed group rather than as separate product-specific counts. Deaths are not reported in the registry record, and no serious adverse event terms are listed.

These figures are event counts, not evidence from a randomized safety comparison. The study was non-randomized, and participants chose a product. The registry record does not provide separate adverse-event counts for people choosing each product or explain whether the recorded events were attributed to a particular product. It also does not provide descriptions of the 14 other adverse events, their timing, or their severity.

General statistical principle: a count of zero recorded events does not, by itself, establish that an event is impossible or that there is no risk. Interpretation depends on the group observed, the completeness of follow-up, and the way events were collected and classified. Those details are not fully reported in the registry record. The figures should therefore be read as the recorded counts for the listed group, without converting them into a claim about comparative safety.

13. What the Result Does, and Does Not, Mean

The trial’s primary measure was designed to describe whether participants who selected naproxen sodium extended release expected their pain to last more than 12 hours. That is a focused question about self-selection and reported expectation. The registry record describes the endpoint calculation and interview process, but does not report the observed percentage or its statistical uncertainty. The primary finding therefore cannot be quantified from the record.

Even if the percentage were available, its meaning would remain bounded by the endpoint definition. It would describe the naproxen-selected subgroup, not all enrolled participants, and it would reflect an expectation reported by participants rather than an assessment of actual pain duration. It would not establish whether a product relieved pain, whether its effect lasted for a particular duration, or whether one product was better than another.

The non-randomized self-selection design is important. Participants chose between naproxen sodium extended release and Advil immediate release, so the choice itself may be associated with expectations or other characteristics. The trial is not a randomized comparison of the products. Neither the endpoint definition nor the available adverse-event counts support a causal claim about comparative treatment effects.

The registry records zero serious adverse events and 14 other adverse events among 237 participants at risk in the listed combined group. Those descriptive counts do not establish a comparative safety profile, particularly because product-specific counts and event descriptions are not reported. The record also does not report deaths.

The central statistical conclusion is about what can and cannot be evaluated. The trial question and primary endpoint are described, but numerical primary and secondary results are not reported in the registry record. Without those results, it is not possible to judge the observed self-selection pattern, its precision, or whether it met the pilot objective. Missing results should not be interpreted as a positive or negative finding.

14. Why This Trial Matters Statistically

This trial is statistically useful as an example of how a study’s endpoint can be shaped by participant choice. The primary measure was not a conventional efficacy contrast between assigned treatments. Instead, it focused on the expectation reported by participants who chose naproxen sodium extended release. Understanding that conditioning is essential to interpreting what the endpoint could answer.

The design also illustrates why the word comparator must be used carefully. Advil immediate release was available alongside naproxen sodium extended release, but allocation was non-randomized and participants selected a product. The presence of two products does not by itself create a randomized controlled comparison. Statistical interpretation must follow the allocation process and the analysis population, rather than assume that product groups are exchangeable.

The endpoint has a specific denominator: naproxen selectors reporting either of the stated expected-duration categories. That denominator differs from the total enrollment and from the number choosing either product. This distinction is broadly important for percentage outcomes. The population to which a percentage applies is determined by its numerator and denominator, not merely by the trial’s enrollment figure.

The record also demonstrates the difference between an endpoint definition and a reported result. The primary calculation is described, but its value and precision are not reported. A well-defined measure does not by itself show what the study found. Similarly, descriptive safety counts should not be converted into comparative claims when allocation is non-randomized and the figures are not separated by product choice.

Finally, the registry lists outcome measures but zero analyses. This highlights the limits of a registry record when analysis results and methods are absent: readers can identify the question and some design features, but cannot evaluate the estimate, uncertainty, missing-data handling, or multiplicity. Careful statistical reporting must make those elements available for interpretation.

15. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The most immediate limitation for interpreting the primary objective is that the registry record does not report the primary endpoint result. It also does not report a confidence interval or other measure of precision. The direction and magnitude of the observed self-selection finding therefore cannot be evaluated. Numerical results for the listed secondary outcomes are also not reported.

The primary analysis was restricted to subjects who chose naproxen sodium. The record does not report how many participants made that choice, so the size of the endpoint denominator and the stability of the estimate cannot be assessed. The endpoint is based on expected pain duration, not on whether the expectation later matched the duration actually experienced.

Allocation was non-randomized, with participants choosing between naproxen sodium extended release and Advil immediate release. This limits the use of the study as a comparative treatment evaluation. The registry record does not report product-specific outcome comparisons, adjustment methods, or a statistical plan that would address differences associated with product selection.

The interview instructions allowed a call within 30 minutes, with participants who did not call interviewed after 14 days. The record does not report the extent of follow-up completion, how incomplete or unavailable responses were handled, or whether sensitivity analyses were conducted. It also does not report details of the selection instructions beyond the available description.

The safety information is limited to the combined listed group, with no product-specific adverse-event breakdown or descriptions of other adverse events. Deaths are not reported in the registry record. The record also does not report a sample-size justification, interim analyses, or an analysis plan. These omissions limit assessment of precision, analysis choices, and the completeness of the reported results.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Self Selection Trial of Naproxen Sodium — NCT01383486.
• Registry record last updated 2015-10-15; status last verified 2015-06.
• Results first posted 2012-11-29.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

19. Record Summary

The registry identifies NCT01383486 as the Self Selection Trial of Naproxen Sodium, a phase 3 completed pilot trial sponsored by Bayer. It lists pain as the condition, non-randomized allocation, no masking, a parallel model, and enrollment of 253. The recorded start was 2011-07, with primary completion in 2011-08.

Participants could choose naproxen sodium extended-release tablets containing 660 mg naproxen sodium or Advil immediate-release caplets containing 200 mg ibuprofen upon a pain episode. The primary endpoint was the percentage of naproxen selectors who expected pain to last more than 12 hours, measured over up to 14 days. The primary endpoint result and numerical secondary outcome results are not reported in the registry record.

The record lists three outcome measures and zero analyses. For the listed combined group, it records zero serious adverse events and 14 other adverse events among 237 participants at risk. Product-specific safety counts and descriptions of the other adverse events are not reported.